1. Field of the Invention
The instant invention relates to the hull design of water-craft. More particularly it relates to the hull design of high-speed water-craft of the planing type as opposed to water-craft with displacement type hulls.
2. Discussion of Prior Art
Planing type hulls for water-craft are generally old and the use of the forward motion of the hull to raise the water-craft partially out of the water and thereby reduce hull to water friction is well understood. Examples of the more highly developed and sophisticated designs are racing hydroplanes and the floats or pontoons of seaplanes. Water-craft of the planing type are quite different from water-craft with displacement hulls. The former are usually lightly constructed and exhibit a relatively flat bottom designed to present an angle of attack to the water when driven at high speed. The force of the water against the flat and angled bottom raises the hull up and out of the water where it will skim over the surface much as a flattened rock when skipped across the water by a child at play. When the speed of the rock decreases below a certain critical speed, the rock sinks. Just so does the planing hull when the applied propulsion power drops below that amount required to keep the water-craft "on plane."
Water-craft of the displacement hull type, as the name suggests, displace a volume of water equal in weight to the total weight of the water-craft. A displacement type hull moving through the water must continuously move this amount of water aside in order to make progress. As speeds increase, the resistance of the water to being moved aside increases drastically until the "hull speed" or that speed beyond which it is impossible to drive the hull regardless of expended power is reached.
A water-craft of the planing type, if driven with sufficient propulsion power to get "on plane", will ride atop the surface of the water without displacing anything near its own weight of water. A water-craft "on plane" can utilize propulsion power to achieve speed.
It is characteristic of conventional planing type water-craft that inordinate amounts of propulsion power must be expended simply to raise the hull partially out of the water and to get the water-craft "on plane". Once the craft is "on plane", the applied driving force at once becomes more effective to produce speed.
It is to the design of planing hulls for water-craft that this invention is directed. An accepted design of demonstrated efficiency for planing hulls is a conventionally developed bow and midship section extending approximately two-thirds of the total hull length. At this point is located the "step", which is simply an abrupt vertical displacement of the bottom from which displacement the trailing one-third of the hull continues aft to the stern.
Operation of the stepped planing hull is simplicity itself. The stepped planing hull is driven forward with sufficient applied propulsion power to achieve a speed such that the upward pressure of the water acting on the submerged bow and midship sections raises the hull to the extent that only those hull sections forward the step ride in the water. At this point not only has the total water displacement of the hull been markedly reduced, but the entire aft one-third of the hull has been lifted and freed from the drag of the water. The hull, riding the water in this particular aspect is said to be, "on the step", or "on plane".
Simple as the stepped planing hull appears to be in execution and mode of operation, certain inherent problems beset the practitioners of planing hull art at the outset.
It was discovered early in stepped-hull development that higher propulsion power seemed to be required just prior to the moment the hull section trailing the step lifted free and the hull went "on plane". Investigation determined that a stubborn vacuum formed immediately aft the step and held the hull so tenaciously to the water at speeds that should have produced planing that it was by no means uncommon for sea-planes to find take-off in smooth water quite impossible. This situation gave rise to the technique of churning up the surface of the water and taking-off across the sea-plane' s own disturbed wake using the induced waves as a means for breaking the hull loose from the water.
Subsequently, it was discovered that air streams could be directed through the planing hull and discharged into the vacuum that developed aft the step-lift of the hull.
U.S. Pat. No. 1,812,265 (Hone, issued June 30, 1931) is one of several inventions directed to the problem of breaking the vacuum that forms immediately after the hull step. This patentee simply employed streams of air diverted through openings in the hull to break the vacuum by the hull step and once this particular function was accomplished the patentee ignored the ultimate fate of the air used to break the vacuum. A somewhat similar patent is U.S. Pat. No. 1,712,281 (Royer, issued May 7, 1929) wherein air streams induced to enter beneath the hull bottom to a location adjacent the hull step are used to eliminate the vacuum induced by the hull step. This particular patentee trapped the air subsequent to its use for breaking the hull step vacuum and created therewith an air cushion between the two pontoons of his speed boat hull with air discharge severely restricted at the stern by means of the sternsheet.
Restriction of air discharge is of course essential if the intent, as here in the present invention, is primarily the provision of an air film for the stern sections of the hull abaft the step.
Other related patents are U.S. Pat. Nos. 3,547,064 (Glass, issued Dec. 15, 1970) and 3,606,857 (Sundquist, issued Sept. 12, 1971). Glass uses an air flow system at the rear of a monohull boat which is, generally speaking, laterally unconfined and does not produce a thin, flat air film flow. Sundquist uses a pressurized air jet propulsion system for a catamaran wherein pressurized air jets flow from the bow all the way along the full length of the hull which is canted upwardly and is not horizontally disposed.
Examples of other air-friction reducing systems for hulls are shown in U.S. Pat. Nos. 1,824,313 (Vogler, issued Sept. 22, 1921) and 1,831,339 (Brush, issued Nov. 10, 1931). Vogler uses a monohull aerating system with longitudinal fins; however there are no outboard fins and the fins do not extend to the stern. Brush uses air bleeder tubes on a hydroplane which put air in only the central portion of the hull, and the central stern portion of the hull thereafter flows upwardly, rather than being flat.
As to catamaran hulls with pivoting hulls, reference is had to U.S. Pat. No. 3,509,842 (Mitchell, issued May 5, 1970).